C基础--猜数字游戏（图形界面由MFC完成）

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <string.h>
#include <ctype.h>


void generate(char computer[])
{
    int i = 0, j, t;

    srand(time(NULL));
    while (i < 4) {
        t = rand() % 10 + '0';
        for (j = 0; j < i; ++j)
            if (t == computer[j])
                break;
        if (j == i) {
            computer[i] = t;
            ++i;
        }
    }
}

int is_valid(char man[])
{
    int i, j;

    if (!(isdigit(man[0])
                && isdigit(man[1])
                && isdigit(man[2])
                && isdigit(man[3])
                && man[4] == ''))
        return 0;
    for (i = 0; i < 3; ++i)
        for (j = i + 1; j < 4; ++j)
            if (man[i] == man[j])
                return 0;
    return 1;
}

int compare(char man[], char computer[])
{
    int i, j, a = 0, b = 0;
    for (i = 0; i < 4; ++i)
        for (j = 0; j < 4; ++j)
            if (computer[i] == man[j] && i == j)
                ++a;
            else if (computer[i] == man[j])
                ++b;
    if (a == 4) {
        printf("YOU BET
");
        return 1;
    }
    if (a == 0 && b == 0) {
        printf("0000
");
        return 0;
    }
    while (a > 0) {
        putchar('A');
        --a;
    }
    while (b > 0) {
        putchar('B');
        --b;
    }
    putchar('
');
    return 0;
}

int usr_input(char array[])
{
        printf("Please input four different letters:
");
        if (scanf("%s", array) != 1) {
            printf("Unkown error!
");
            return 1;
        }
        return 0;
}
void exit_output(char computer[])
{
        printf("The answer is: %c%c%c%c
", computer[0], computer[1], computer[2], computer[3]);
}
void err_output(char str[])
{
        printf("%s
", str);
}
int main(void)
{
    char computer[100];
    char man[100];
    generate(computer);
    while (1) {
        usr_input(man);
        if ((strcmp(man, "EXIT") == 0) || (strcmp(man, "exit") == 0)) {
            exit_output(computer);
            return 0;
        }
        if (!is_valid(man)) {
            err_output("Invalid input!");
            continue;
        }
        if (compare(man, computer))
            return 0;
    }
}